1. Field of the Invention
The present invention relates to an image pickup device provided with pixels in a bayer array.
2. Related Art
Conventionally, in a color camera using a CMOS image sensor, it is general to use a color filter of a so-called bayer array in which filters with primary colors of red (R), green (G) and blue (B), hereinafter collectively called RGB, are arranged in a checkerboard pattern. In the bayer array, G pixels are arranged first in a checkerboard pattern and, in the remaining portions, and then R pixels and B pixels are respectively arranged in checkerboard patterns.
On the other hand, an image sensor in order to improve signal to noise ratio by replacing one of the G pixels with a white (W) pixel to increase light transmission has recently been introduced (see Reference Document 1: A novel Bayer-like WRGB color filter array for CMOS image sensors by Hiroto Honda, et al., Proceedings of SPIE-IS&T Electronic Imaging, SPIE Vol. 6492, pp. 64921J-1 to 64921J-10 (2007); Reference Document 2: High Sensitivity Color CMOS Image Sensor with WRGB Color Filter Array and Color Separation Process using Edge Detection by Hiroto Honda, et al., 2007 International Image Sensor Workshop, Jun. 7-10, 2007; and Reference Document 3: News Release from Eastman Kodak, Jun. 14, 2007).
In Reference Document 1 and Reference Document 2, in order to improve signal to noise ratios of RGB signals, RGB pixel values (RW, GW and BW) at the pixel position of W pixels in this color filter array are generated based on the following Equations 1 to 3.RW=W×R-average/(R-average+G-average+B-average)  Equation 1GW=W×G-average/(R-average+G-average+B-average)  Equation 2BW=W×B-average/(R-average+G-average+B-average)  Equation 3
Here, an R-average is calculated by averaging two R pixels neighboring a W pixel. Similarly, a B-average is calculated by averaging two B pixels neighboring the W pixel and a G-average is calculated by averaging four G pixels neighboring the W pixel.
Since Reference Document 1 to Reference Document 3 assume the use of an image sensor having W pixels, the sensor cost is likely to become high. Further, since an existing sensor with a bayer array can not be used, it is likely to take time to gain popularity, and verification of electrical characteristics of the sensor having W pixels is also required. Particularly, there may be also various problems associated with sensitivity differences between W pixels and other pixels and variations in filter characteristics and such.